Calibrating voltage generator

ABSTRACT

A device for providing a precise calibrating voltage permitting of adjustment to high resolution and great linearity, in which to avoid their influence contact resistances only occur in circuits with current sources.

United States Patent [19] 11] 3,766Afii Bolk 1 Oct. 16, 1973 CALIBRATING VOLTAGE GENERATOR R [75] Inventor: Willem Thomas Bolk, Zeist,

Netherlands [56] References Cited [73] Assignee: Nederlandse Optiek-en UNITED STATES PATENTS Instrumentenfabriek Dr C E' Berry Bleeker N31. Zeist, Netherlands 3,419,906 12/1968 Umantsev 324/98 [22] Filed: May 1972 Primary Examiner-Robert K. Schaefer [21] App]. 252 000 Assistant ExaminerMorris Ginsburg Attorney-Arthur B. Colvin [30] Foreign Application Priority Data [57] ABSTRACT May 11, i971 Netherlands 7106416 A device for providing a precise calibrating voltage permitting of adjustment to high resolution and great g 26 linearity, in which to avoid their influence contact re- [581 Fieid 18 sistances only occur in circuits with current sources.

2 Claims, 1 Drawing Figure CALIBRATING VOLTAGE GENERATOR The invention relates to a device for providing a precise calibrating voltage permitting of adjustment to high resolution and great linearity, which device has between its two terminals a plurality of groups of resistances, the resistances in each group being equal to each other but different from those of the other groups.

In many devices such as, for instance, compensators and digital voltmeters, it is desirable that means be provided whereby a very precise and time-constant calibrating voltage can be adjusted. Devices of the aforementioned kind, such as Dieselhorst circuits and Raps circuits, are so contrived that in cases where contact resistances varying with time and thermal E.F.F.s are operative in switches, their functioning enters as little as possible into the measuring results obtained with these circuits, whilst in cases where the influence of contact resistances and thermal E.M.F.s cannot be avoided, use is made of very good and hence expensive switches.

The object of the invention is to provide a device in which the influence of contact resistances and thermal E.M.F.s is practically ruled out.

The device according to the invention is for this purpose characterized in that the resistances are connected in series and that a plurality of current sources is provided which deliver currents I, l/ 100 I, 1/ 10,000 I, etc. and which can be connected over several of the resistances.

The invention will be described by reference to the drawing.

The FIGURE shows a preferred embodiment of the device according to the invention.

The device depicted contains a group of nine resistances R and a group of nine resistances R, which are connectable in series between two terminals 27 and 28. Moreover, two current sources for currents I and 1/100 I are provided which are connected respectively at 19, 20 and at 21, 22 to rails 23, 24 and 25, 26 respectively. Further connections, e.g. by means of switches, can be established between these rails and the terminal points 0 to 18 inclusive. If, for instance connections have been made between terminal point 16 and rail 23; between terminal point 7 and rail 24; between rail 26 and terminal point 2; and between rail 25 and terminal point 17, the voltage measured between terminals 27 and 28 is:

It is evident that the contact resistances and thermal E.M.F.s between the terminal points and the rails will only occur in circuits in which current sources are incorporated. They then hardly enter into account, since theoretical current sources have infinite resistance whilst practical current sources have a very high interla resistance. Morever, it is to be observed that the internal as to accuracy of the current source delivering a current of l/ I need not be so stringent as in the case of a current source delivering a current I. Higher resolution is achievable by connectinga third current source for 1/ 10.000 I; in this way a calibrating voltage can be provided which is adjustable for still higher resolution.

What I claim is:

l. A device for providing a permitting of adjustment to high resolution and great linearity, which device comprises two terminals, a plurality of groups of resistances between said two terminals, the resistances in each group being equal to each other but different from those of the other groups, characterized in that means are provided to connect the resistances in series and a plurality of current sources having high internal resistances is provided which deliver currents I, l/ 100 I, 1/ 10,000 I, etc, and means to connect said current sources over several of the resistances so that the influence of contact resistances and thermal E.M.F.s is practically ruled out.

2. A device according to claim 1 containing two groups of resistances each having nine resistances, those in one group differing from those in the other group by a factor of 10, CHARACTERIZED in that there are two current sources, one fora current I and one for a current 1/100 I.

precise calibrating voltage 

1. A devicE for providing a precise calibrating voltage permitting of adjustment to high resolution and great linearity, which device comprises two terminals, a plurality of groups of resistances between said two terminals, the resistances in each group being equal to each other but different from those of the other groups, characterized in that means are provided to connect the resistances in series and a plurality of current sources having high internal resistances is provided which deliver currents I, 1/100 I, 1/10,000 I, etc, and means to connect said current sources over several of the resistances so that the influence of contact resistances and thermal E.M.F.''s is practically ruled out.
 2. A device according to claim 1 containing two groups of resistances each having nine resistances, those in one group differing from those in the other group by a factor of 10, CHARACTERIZED in that there are two current sources, one for a current I and one for a current 1/100 I. 